The present invention relates to a system for controlling flow in turbomachinery and particularly relates to a control system for ejectors used to provide cooling and/or purge flow to turbine components.
In gas turbines, a portion of the total air flow from the compressor inlet is diverted to various turbine components for various purposes, including cooling those components. The diverted air can consume a large proportion of the total air flow through the compressor, for example, as much as 20%. The management and control of these parasitic flows can dramatically increase the performance of the turbine. Typically, air under pressure is extracted from the compressor and bypasses the combustion system of the turbine for use as a cooling flow for various turbine components. Ejectors are often used for this purpose. For example, bleed air may be extracted from the thirteenth stage of the compressor for flow to the second stage nozzle to cool the nozzle. Bleed air is also extracted from another stage, for example, the ninth stage, at a lower pressure and temperature than extracted from the thirteenth stage for supplying cooling air to the third stage nozzle. The extraction ports often provide cooling air flow at too high a pressure and/or temperature and typically the flow is throttled, resulting in a net loss of energy. By employing an ejector, the low pressure/temperature flow may be mixed with the high pressure/temperature flow to provide a flow at an intermediate pressure and temperature substantially matching the pressure and temperature required to cool a turbine component, while simultaneously making use of low pressure and temperature air which otherwise might be dissipated as wasted energy.
Ejectors, however, have no moving parts and are designed for operation at specific design points based on ISO day conditions. For turbine applications, the turbine inlet conditions to the ejector are a function of ambient day conditions in which the turbomachinery operates. The ambient day variations seen by the gas turbine can vary from xc2x0F. to 120xc2x0 F., which results in about a 35% temperature and about 20% pressure variation on the inlet/exit conditions to the ejector. This variation has a strong effect on the operational characteristics of the ejector to the extent that, at many ambient day conditions, the ejector will not provide adequate cooling and/or purge flow. That is, the ejector behaves differently on different days and at different times during each day. On certain days, the ejector will provided insufficient benefit or too much benefit.
In accordance with a preferred embodiment of the present invention, there is provided, in a cooling system having an ejector for supplying fluid at a pressure and temperature intermediate the pressure and temperature of each of first and second flows, a control system affording the capability of changing the flow characteristics of the ejector. That is, the control system hereof, in various forms, controls the primary inlet and the secondary inlet to and/or exit conditions from the ejector whereby the operating characteristics of the ejector can be controlled. Additionally, bypass piping may be included as part of the control system such that, under certain conditions, the ejector may be bypassed and the cooling flow provided under conventional turbine operating conditions. Thus, the present control system enables ejectors to be incorporated in gas turbine designs or as components for upgrades to existing turbines where they would not normally be considered due to the inherent fluctuation in flow characteristics through the ejectors, up to and including failure to deliver adequate cooling and/or purge flow, and for risk abatement or nearoperation.
More particularly, and in one form of the invention, the control system may be placed on the suction side of the ejector, the outlet side of the ejector or preferably both the suction and outlet sides of the ejector. In each case, the control system includes a control or throttling valve, a sensor, i.e., a pressure transducer, and a controller. The flow characteristics through the flow line, for example, the suction line to the ejector, are sensed by the pressure transducer and the controller controls the control/throttling valve in accordance with a compared difference between the sensed flow characteristics and predetermined flow characteristics whereby the flow is controlled. It will be appreciated that the sensed flow characteristics are a function of ambient conditions and, consequently, the control of the flow is a function of ambient conditions. An additional set of these components is preferably provided on the outlet side of the ejector as well to afford total control over the ejector and provide control which matches the sensitivity of the gas turbine. Additionally, a flow line bypassing the ejector is provided with a control valve in the bypass line. The bypass line affords the ability to override the ejector and/or supplement the cooling/purge flow for risk abatement or nearoperation.
In a second embodiment of the present invention, a similar control system comprised of a flow sensor, a throttling valve and a controller is provided on the motive and exit sides of the ejector. A bypass flowpath is also provided between the motive and exit flowpaths. In a third embodiment, the control system employs a flow sensor, a throttling valve and a flow controller on the inlet side of the ejector, with a shutoff valve on either the exit side of the ejector or the suction side of the ejector. In all of these embodiments, the operating characteristics of the ejector are controlled and accommodate the change in the ambient day conditions.
In a preferred embodiment according to the present invention, there is provided a method for controlling flow in turbomachinery, comprising the steps of establishing a first fluid flow in the turbomachinery and flowing the first fluid flow to a first site on the turbomachinery, establishing a second fluid flow in the turbomachinery at a pressure and temperature lower than the pressure and temperature of the first flow and flowing t he second fluid flow to a second site on the turbomachinery, selectively combining at least a portion of the second flow with the first flow through a crossover path to provide a third fluid flow to the first site at a pressure and temperature intermediate the pressure and temperature of the first and second flows, respectively, sensing a characteristic of the flow through the crossover path and controlling the flow through the crossover path in accordance with the sensed flow characteristics of the flow through the crossover path.
In a further preferred embodiment according to the present invention, there is provided a method for controlling flow in turbomachinery, comprising the steps of establishing a first fluid flow in the turbomachinery and flowing the first fluid flow to a first site on the turbomachinery, establishing a second fluid flow in the turbomachinery at a pressure and temperature lower than the pressure and temperature of the first flow and flowing the second fluid flow to a second site on the turbomachinery, selectively combining at least a portion of the second flow with the first flow through a crossover path to provide a third fluid flow to the first site at a pressure and temperature intermediate the pressure and temperature of the first and second flows, respectively, sensing a characteristic of the combined flow to the first site and controlling the combined flow to the first site in accordance with the sensed characteristics of the combined flow.
In a further preferred embodiment according to the present invention, there is provided a method for controlling flow in turbomachinery, comprising the steps of establishing a first fluid flow in the turbomachinery and flowing the first fluid flow to a first site on the turbomachinery, establishing a second fluid flow in the turbomachinery at a pressure and temperature lower than the pressure and temperature of the first flow and flowing the second fluid flow to a second site on the turbomachinery, selectively combining at least a portion of the second flow with the first flow through a crossover path to provide a third fluid flow to the first site at a pressure and temperature intermediate the pressure and temperature of the first and second flows, respectively, sensing a characteristic of the first fluid flow before combining the first flow and second flow portion and controlling the first flow in accordance with the sensed flow characteristics of the first flow before combining the first flow and the second flow portion.
In a further preferred embodiment according to the present invention, there is provided a system for bleeding air from plural ports in a multicompressor to provide cooling and/or sealing air to an associated turbine site for optimizing turbine performance, comprising a first extraction port for extracting a first flow from a pressure stage of the compressor for flow along a first flowpath, a second extraction port for extracting a second flow from another pressure stage of the compressor for flow along a second flowpath and at a pressure and temperature lower than the pressure and temperature of the first flow, a first crossover flowpath interconnecting the first flow along the first flowpath and the second flow along the second flowpath to provide a crossover flow therebetween, an ejector having an inlet for receiving the first flow along the flowpath and a second inlet for receiving the crossover flow from the second flowpath, a mixer and a diffuser for respectively combining the first flow and crossover flow to provide a third combined flow along a third flowpath, a control valve for controlling the flow through one of the first flowpaths, the crossover flowpath and said third flowpath, a sensor for sensing a characteristic of one of the first, second and third flows and a controller for controlling the flow through the control valve in accordance with the sensed flow characteristic of the one flow enabling the combined first and crossover flows for flow to a first site of the turbine at a pressure and temperature intermediate the temperature and pressure of the first and second flows.